BERLIN (Reuters) - A painstaking two-year investigation to determine which of two skulls belonged to Friedrich Schiller has found neither is a match, prolonging a 180-year-old mystery over the celebrated German poet's remains. A team of international experts came to their surprise conclusion after comparing DNA samples from the two skulls in question to material from the graves of the poet's relatives.

"The investigations into the relics which have been attributed to Friedrich Schiller have proven that neither of the skulls is authentic," said a statement released by the Weimar Foundation and MDR broadcaster who had supported the research.

German anthropologists from Berlin and Freiburg had initiated the project and earlier this year they exhumed the graves of several of Schiller's family members in southern Germany.

The puzzle over the skull began in 1826, 21 years after Schiller died when the mayor of Weimar had 23 skulls dug up from a mass grave in which the poet was buried.

The mayor identified the biggest skull and one which bore a resemblance to the dramatist's death mask as Schiller's and it was brought to the home of his contemporary Goethe before being buried in a crypt in the eastern city of Weimar.

Later, Goethe's tomb was placed next to Schiller's in the crypt which still attracts about 41,000 visitors a year. Schiller had spent the last years of his life in Weimar which is mostly famous for being Goethe's home for almost 50 years.

However, in 1911, another skull was retrieved from the mass grave and researchers claimed that was the real one, sparking a lengthy dispute amongst academics, historians and anthropologists about the origin of the two skulls.